Metallocene catalysts which are known as homogeneous catalysts for the polymerization of .alpha.-olefin, can show a high polymerization activity and are capable of producing a polymer with a narrow molecular weight distribution. In particular, when using a stereorigid transition metal complex containing a ligand having such a structure that two cyclopentadienyl groups are cross-linked with each other, it is possible to obtain isotactic polypropylene (e.g., refer to "Journal of American Chemical Society", Vol. 106, p. 6355, etc.).
Further, it is also known to obtain polypropylene having a high isotacticity by using a transition metal complex having such a structure that two cyclopentadienyl groups are cross-linked with each other by a silicon atom (e.g., refer to Japanese Patent Application Laid-Open (KOKAI) Nos. 63-295607 -and 1-275609, etc.).
In addition, in order to enhance the isotacticity and molecular weight of polypropylene, it is known to use compounds having an indenyl group as a part of a ligand thereof into which a substituent group is introduced (e.g., refer to Japanese Patent Application Laid-Open (KOKAI) Nos. 4-268307 and 6-157661, etc.).
On the other hand, for example, from Japanese Patent Application Laid-Open (KOKAI) No. 2-76887, it is also known to obtain isotactic polypropylene by using a transition metal complex having such a structure in which two cyclopentadienyl groups are cross-linked with each other by a silicon atom or a germanium atom.
The above-mentioned cyclopentadienyl compounds as a ligand of the transition metal complex which are cross-linked by a silicon atom or a germanium atom, can be usually produced by reacting (i) an alkali metal salt or an alkali earth metal salt of a cyclopentadienyl compound with (ii) a halogenated silicon compound or a halogenated germanium compound.
For instance, Jutzi et al. have reported that upon producing dimethyl bis(tetramethylcyclopentadienyl) silane, tetramethylcyclopentadienyl lithium and dichlorodimethyl silane are heat-refluxed in tetrahydrofuran (THF) as a solvent for 5 days, and that the yield is 65% (refer to "Chemische Berichte", vol. 119, p. 1750).
In addition, Winter et al. have reported that upon producing dimethyl bis(2-methyl indenyl) silane, a lithium salt of 2-methyl indene was dropped into a diethyl ether solution of dichlorodimethyl silane for 5 hours and then stirred overnight at room temperature, and further allowed to stand for a weekend period, and that the yield was 16% (refer to Japanese Patent Application Laid-Open (KOKAI) No. 4-268307).
On the other hand, there is also known such improved techniques for efficiently producing two cyclopentadienyl compounds which are cross-linked with each other by a silicon atom or a germanium atom. For instance, in Japanese Patent Application Laid-Open (KOKAI) No. 7-252287, it has been taught that in order to enhance the yield of a compound having two cyclopentadienyl groups cross-linked with each other by a silicon atom, a substituted cyclopentadiene is reacted with dimethyl dihalosilane under the coexistence of a metal salt-type base and a metal ion-capturing agent. As such metal ion-capturing agents, there are known, for example, N,N,N',N'-tetramethyl ethylene diamine or the like (Japanese Patent Application Laid-Open (KOKAI) No. 6-279477).
Further, in Japanese Patent Application Laid-Open (KOKAI) No. 6-271594, it has been described that a lithium salt, a sodium salt or a potassium salt of a cyclopentadienyl compound is reacted with a halogenated silicon compound or a halogenated germanium compound in the presence of a cyanide or a thiocyanate, thereby enhancing the yield.
In order to obtain the above cyclopentadienyl compounds which are cross-linked by a silicon atom or a germanium atom, it is necessary to conduct the reaction for a long period of time as described above. In addition, the yield is not necessarily satisfactory. In particular, in the case where two or more sterically bulky substituent groups are bonded to the silicon atom or the germanium atom, the above disadvantageous tendency becomes more remarkable, thereby further deteriorating the yield.
In general, production processes showing a poor yield require large costs for purifying the reaction products, resulting in economical disadvantages. In addition, in the case where the metallocene compound is produced from a low-purity compound as a raw material, the purity of the obtained metallocene compound also becomes low, and the purification of the compound also requires large costs.
As described above, the conventional techniques for improving the yield of the cyclopentadienyl compound cross-linked by a silicon atom or a germanium atom, are still unsatisfactory in effects thereof, and further require the use of harmful compounds such as cyanides which tend to exhibit a toxicity to human bodies, etc. Accordingly, if such a production process capable of producing the cyclopentadienyl compound cross-linked by a silicon atom or a germanium atom with a high yield, could be established by using harmless compounds, the process is industrially advantageous.